Dimensioning includes measurements, notes, and symbols.
Dimensions can be inside the lines, or at the end of a leader that points at the space between the lines.
All diameter measurements must have the fillet symbol, and all radius measurements must have the R symbol. Radius measurements should be only used for arcs, fillets, and rounds, not full circles.
When dimensioning radii that join perpendicular lines, the dimensions do not have to indicate the centre. If it is not connecting parallel lines, the centre must be indicated.
Base imperial unit is inch. Inches omit leading zeros, but not trailing zeros. Base metric unit is millimeters. Millimeters keep leading zeros, but omit trailing zeros. E.g. .250", 0.25mm.
Dimensions should not be duplicated (closing dimensioning chain). Always try to give the minimum number of dimensions. Dimensions should be placed in the view where the best shape and true form are shown. Avoid long extension and leader lines. Place dimensions between views when possible, especially if it applies to both views. This can improve the drawing's clarity. Do not assume that a part is symmetrical, dimension both sides of a symmetrically shaped object, or use the center line to show that it is symmetrical. Spacing between dimensions should be consistent within a drawing. Line up dimensions horizontally and vertically, where possible.Avoid crossing dimension lines and leader lines when possible. Make full use of notes, abbreviations, and symbols to show how many times a dimension applies. For example, use 2X in a mote to designate that a detail specified in a note exists in two places.